The Jemaah Islamiah group said in a purported statement carried on the Internet, that it carried out the attack on the Australian embassy in Jakarta, and warned of more further attacks if fails to Australia withdraws its forces from Iraq.
"We decided to make Australia pay in Jakarta today when one of the Mujahideen brothers carried out a martyrdom operation at the Australian embassy," the statement from the "al-Jama'a al-Islamiya in East Asia" said.
It was not immediately possible to verify the claim which appeared in a public Web forum which has sometimes carried claims from Islamic groups which turned out to be false.
The al Qaeda-linked network has been blamed for previous blasts in Indonesia such as the Bali bomb attacks in 2002 that killed 202 people, including 88 Australians.
It was also accused of a suicide bomb blast at Jakarta's Marriott Hotel in August 2003 that killed 12 people.
The group does not usually post statements on Arabic Web sites which have become popular among insurgents fighting US troops and their allies in Iraq over the last year.
"We advise all Australians to get out of Indonesia, or we will make it a grave for them ... and the Australian government ... if it does not, we will direct a number of painful blows," the statement said.
Meanwhile, Ayman al-Zawahri, the number two figure in al Qaeda, appeared in a new videotape aired on Al Jazeera television this evening, saying US forces are stuck in a quagmire in Iraq and Afghanistan.
"In both countries, if they continue they will bleed to death and if they withdraw they lose everything," said Zawahri, the right-hand man of al Qaeda leader Osama bin Laden.
"East and south Afghanistan have become an open arena for the Mujahideen. The enemy are limited to their capitals," the native Egyptian said.
"The Americans are hiding in their trenches and refuse to come out to face the Mujahideen, as the Mujahideen shell and fire on them, and cut roads off around them. Their defence is only to bomb by air, wasting US money as they kick up dust."
Zawahri, wearing a white turban with a machine gun at his side, spoke to camera for several minutes.
He said fighters in Iraq had turned Washington's plans for the oil-rich country "head-over-heels".